1. Field of the Invention
This invention is directed to novel compounds and polymeric compositions containing such novel compounds. More specifically, this invention concerns itself with a new class of stabilizer for polyolefins and stabilized polymeric materials which are resistant to oxidative degradation and possess enhanced stability even after prolonged exposure to ultraviolet light.
2. Description of the Prior Art
Polymers have in the past and continue to provide an attractive substitute for other more traditional types of structural materials (e.g. wood and metals) because of relatively inexpensive materials and fabrication costs. As polymers continue to find new applications in, for example, the fabrication of automotive parts and building materials, they must also become more durable and capable of withstanding prolonged exposure to a variety of degradative forces. Degradation of polymers can be caused by exposure to light, heat and/or air. Such degradation is usually manifest by either a partial or total loss of structural integrity, changes in light transmission properties, changes in color, loss or reduction in flexibility and/or resiliency, or any combination of the above phenomena. Those attempting to avoid polymer degradation have generally selected from among three possible approaches: (a) elimination or reduction of the degradative forces; (b) isolation of the sensitive polymer material from the degradative forces; or (c) modification of the polymer composition to enhance its resistance to the degradative forces. The latter approach is generally preferable since it does not require elaborate engineering or structural changes in the polymer product environment.
There are a variety of additives which have been disclosed as suitable for enhancing the resistance of polymers to one or more of the degradative forces discussed hereinabove. These additives (hereinafter referred to as "stabilizers") can be physically combined with or engrafted upon the environmentally sensitive polymer, thereby prolonging its useful life in the hostile degradative environment. Stabilizers are available which can enhance the polymer's resistance to one or more of the degradative forces discussed hereinabove and conversely, a stabilizer which is effective for prevention of, for example, oxidative degradation may have little if any effect upon the polymers resistance to other degradative agents. Thus, it is not uncommon for polymers to contain a variety of stabilizer materials, each being present for the prevention of a particular degradative reaction.
One of the more difficult to control of the degradative reactions results from exposure of the polymer to the oxygen present in the atmosphere. The impact of such exposure will, of course, vary upon temperature prevailing at the time of such exposure and the presence or absence of other agents either within the polymeric material or in contact with the polymeric material which can accelerate such degradation. Ordinarily, the effects of oxidation manifest themselves only after a prolonged interval and repeated exposure. The exposure of polymers to the degradative forces of oxidation can result in a variety of changes in such materials depending upon the degree of saturation of the polymer backbone and the various substituents pendant from the backbone. The oxidative degradation of polyolefins and dienic polymers is, however, mechanistically distinct, thus a stabilizer which is effective for prevention of oxidative degradation of polyolefins will in all likelihood be ineffective to impart similar protection to dienic polymers.
A number of materials are presently commercially available which are highly effective in the stabilization of polyolefins against oxidative degradation. Among the more prominently mentioned are Goodrite 3125 (a triester of a substituted cinnamic acid and 1,3,5-tris[2-hydroxyethyl]-s-triazine-2,4,6 trione, available from The B.F. Goodrich Company) and Plastinox 1729 (a diester of a partially hindered mercaptophenol and 1,4-benzenedicarboxylic acid, availabe from American Cyanamid Company). As is true of all additives to polymeric materials, stabilizing agents must be compatible with the host resin and have a minimum of impact upon the processing characteristics of the resin when present therein at concentrations necessary to impart the desired stabilizing characteristic. In addition, such additives and stabilizers should not change the color characteristics, clarity, or other aesthetic properties of the resin in which they are used. As will be appreciated, the latter requirements are only of importance where the stabilized polymer composition is used in the environment where retention of its original appearance is important.
In addition to its compatibility in the host polymer resin, stabilizers must be effective at relatively low concentrations and remain relatively immobile within the stabilized composition during the useful lifetime of the polymeric material. Where stabilizers are free to migrate within the polymer or are volatile at relatively low temperatures, such mobility can result in anisotropic redistribution of the stabilizer within the host polymer or the total loss of the stabilizer from the polymer. In either event, portions of the polymer will be rendered vulnerable to attack by degradative agents and thus the effectiveness of the stabilizer lost.
As is apparent from the above discussion, polymer stabilization against oxidative degradation has been and continues to present serious problems. Although there are a number of materials which are both effective and commercially available to stabilize the polymers against the degradative action of oxygen in the surrounding environment, such agents may, for one reason or another, be incompatible with other compounding ingredients or lack the chemical stability required of such materials (this latter criteria being critical where aesthetic appearance is important).
Thus, there is a continuing need for antioxidants which are both effective for preventing oxidative degradation of polymeric materials and yet compatible with processing and end use requirements of the resin.